The present invention relates to a binary refrigeration unit constituted by comprising a high-temperature side refrigerant circuit and a low-temperature side refrigerant circuit.
As a refrigeration unit of this type, for example, as shown in FIG. 6, there is well-known a binary refrigeration unit 100X which is constructed in such a manner that an evaporator 4 as a refrigerant evaporation section of a high-temperature side refrigerant circuit H constituted by serially connecting a compressor 1, a condenser 2, a pressure reducing valve 3 and the evaporator 4, and a condenser 12 as a refrigerant condensation section of a low-temperature side refrigerant circuit L constituted by serially connecting a compressor 11, the condenser 12, a pressure reducing valve 13 and an evaporator 14 are disposed side by side, a refrigerant of the low-temperature side refrigerant circuit L is cooled to be condensed at the condenser 12 by vaporization heat of a refrigerant of the high-temperature side refrigerant circuit H evaporated by the evaporator 4, the condensed refrigerant of the low-temperature side refrigerant circuit L is evaporated at the evaporator 14, and accordingly a low temperature much lower than a low temperature obtained by the evaporator 4 of the high-temperature side refrigerant circuit H is obtained by the evaporator 14 of the low-temperature side refrigerant circuit L (e.g., see Japanese Patent Application Laid-Open No. 2001-91074).
Regarding the low-temperature side refrigerant circuit L, there is well-known a constitution in which a refrigerant tank 17 is connected to its low-pressure side as indicated by a broken line, i.e., a refrigerant suction side of the compressor 11, through a connecting pipe 16 by interposing a capillary tube 15 as pressure reduction means (e.g., see Japanese Patent Application Laid-Open No. 2001-40340).
In the conventional binary refrigeration unit 100X, as shown in FIG. 7, all the devices which constitute the high-temperature side refrigerant circuit H and the low-temperature side refrigerant circuit L are stored in a device storage section of a case 50 formed to a size smaller than a general size of a doorway, e.g., a size of about 770 mm in width, about 900 mm in depth and about 2000 mm in height, so as to be easily carried through a doorway of a general building into a laboratory, a storage room for storing bacteria, blood components, bone marrow, clinical reagents, fungal threads, various cells, sperms, fertilized eggs, nucleic acids, etc., in a cooled state or the like.
A heat exchanger in which the evaporator 4 of the high-temperature side refrigerant circuit H and the condenser 12 of the low-temperature side refrigerant circuit L are disposed side by side to be integrated so as to enable heat exchange between the refrigerants as shown in FIGS. 6, 7 is called as a cascade capacitor.
In the conventional binary refrigeration unit 100X, if the predetermined amount of a nonfluorocarbon refrigerant in which a boiling point is, e.g., about −40° C. per atmospheric pressure, for example, a mixed refrigerant (mass ratio of 94:6) of R407D (15 mass % of R32 (difluoromethane: CH2F2), 15 mass % of R125 (pentafluoroethane: CHF2CF3), 70 mass % of R134a (tetrafluoroethane: CH2FCF3)) and pentane, is sealed in the high-temperature side refrigerant circuit H in order to obtain a low temperature of about −40° C. by the evaporator 4 of the high-temperature side refrigerant circuit H, in the case of a reciprocation type of the compressor 1 which reciprocates a piston in a cylinder to compress the refrigerant, stop equilibrium pressure (pressure when pressure of the refrigerant suction side and pressure of a refrigerant discharge side become equal to each other) reaches even 734 kPa at +35° C. of outside air. If the refrigerant is compressed by the compressor 1, peak pressure of the refrigerant discharge side reaches 2.7 MPa. Consequently, the compressor 1 cannot be started unless motor torque is sufficiently large (in a state in which a temperature of the evaporator is sufficiently reduced, i.e., when the refrigerant smoothly passes through an expansion valve, conveying resistance of the refrigerant is greatly reduced, and thus the compressor is rotated even by small torque).
Accordingly, in the conventional binary refrigeration unit, the compressor equipped with a large motor is used, and there are inconveniences such as (1) large power consumption and (2) large noise. Thus, there is a need to enable starting of even a compressor equipped with a small-torque and compact motor, and this has been a task to be achieved.